Decay of vortex rings in flexible-walled confined domains

Vortex rings within radially confined domains (rigid tubes) have been the subject of few recent studies (Stewart et al., Exp. Fluids 53, 2012; Danaila et al., J. Fluid Mech. 774, 2015). However, these studies did not consider the effects of including: 1) wall flexibility, and 2) both radial and axial confinement (tubes were left open at the farthest end from the orifice). An example of confined vortex ring propagation under these complexities is observed during the filling of blood in the human cardiac left ventricle. We experimentally investigated laminar vortex ring propagation in confined domains with passively expanding flexible walls. Vortex ring circulation in rigid tubes of varying diameters were compared with Stewart et al. (2012) to verify our methods. PIV measurements were conducted on flexible-walled silicone models of three geometries imposing radial and axial confinement: hemisphere, semi-prolate spheroid, semi-oblate spheroid. Three levels of wall stiffness were considered for each geometry. Though the formation process was nearly unaffected for a particular geometry, we observed higher rate of decay of circulation with increasing wall stiffness. The effects of varying ejection duration and Reynolds number on the decay of circulation will be discussed.